rocksdb/db/merge_helper.h
mrambacher 12f1137355 Add a SystemClock class to capture the time functions of an Env (#7858)
Summary:
Introduces and uses a SystemClock class to RocksDB.  This class contains the time-related functions of an Env and these functions can be redirected from the Env to the SystemClock.

Many of the places that used an Env (Timer, PerfStepTimer, RepeatableThread, RateLimiter, WriteController) for time-related functions have been changed to use SystemClock instead.  There are likely more places that can be changed, but this is a start to show what can/should be done.  Over time it would be nice to migrate most (if not all) of the uses of the time functions from the Env to the SystemClock.

There are several Env classes that implement these functions.  Most of these have not been converted yet to SystemClock implementations; that will come in a subsequent PR.  It would be good to unify many of the Mock Timer implementations, so that they behave similarly and be tested similarly (some override Sleep, some use a MockSleep, etc).

Additionally, this change will allow new methods to be introduced to the SystemClock (like https://github.com/facebook/rocksdb/issues/7101 WaitFor) in a consistent manner across a smaller number of classes.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7858

Reviewed By: pdillinger

Differential Revision: D26006406

Pulled By: mrambacher

fbshipit-source-id: ed10a8abbdab7ff2e23d69d85bd25b3e7e899e90
2021-01-25 22:09:11 -08:00

198 lines
8.0 KiB
C++

// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
//
#pragma once
#include <deque>
#include <string>
#include <vector>
#include "db/dbformat.h"
#include "db/merge_context.h"
#include "db/range_del_aggregator.h"
#include "db/snapshot_checker.h"
#include "rocksdb/compaction_filter.h"
#include "rocksdb/env.h"
#include "rocksdb/slice.h"
#include "util/stop_watch.h"
namespace ROCKSDB_NAMESPACE {
class Comparator;
class Iterator;
class Logger;
class MergeOperator;
class Statistics;
class SystemClock;
class MergeHelper {
public:
MergeHelper(Env* env, const Comparator* user_comparator,
const MergeOperator* user_merge_operator,
const CompactionFilter* compaction_filter, Logger* logger,
bool assert_valid_internal_key, SequenceNumber latest_snapshot,
const SnapshotChecker* snapshot_checker = nullptr, int level = 0,
Statistics* stats = nullptr,
const std::atomic<bool>* shutting_down = nullptr);
// Wrapper around MergeOperator::FullMergeV2() that records perf statistics.
// Result of merge will be written to result if status returned is OK.
// If operands is empty, the value will simply be copied to result.
// Set `update_num_ops_stats` to true if it is from a user read, so that
// the latency is sensitive.
// Returns one of the following statuses:
// - OK: Entries were successfully merged.
// - Corruption: Merge operator reported unsuccessful merge.
static Status TimedFullMerge(
const MergeOperator* merge_operator, const Slice& key, const Slice* value,
const std::vector<Slice>& operands, std::string* result, Logger* logger,
Statistics* statistics, const std::shared_ptr<SystemClock>& clock,
Slice* result_operand = nullptr, bool update_num_ops_stats = false);
// Merge entries until we hit
// - a corrupted key
// - a Put/Delete,
// - a different user key,
// - a specific sequence number (snapshot boundary),
// - REMOVE_AND_SKIP_UNTIL returned from compaction filter,
// or - the end of iteration
// iter: (IN) points to the first merge type entry
// (OUT) points to the first entry not included in the merge process
// range_del_agg: (IN) filters merge operands covered by range tombstones.
// stop_before: (IN) a sequence number that merge should not cross.
// 0 means no restriction
// at_bottom: (IN) true if the iterator covers the bottem level, which means
// we could reach the start of the history of this user key.
// allow_data_in_errors: (IN) if true, data details will be displayed in
// error/log messages.
//
// Returns one of the following statuses:
// - OK: Entries were successfully merged.
// - MergeInProgress: Put/Delete not encountered, and didn't reach the start
// of key's history. Output consists of merge operands only.
// - Corruption: Merge operator reported unsuccessful merge or a corrupted
// key has been encountered and not expected (applies only when compiling
// with asserts removed).
// - ShutdownInProgress: interrupted by shutdown (*shutting_down == true).
//
// REQUIRED: The first key in the input is not corrupted.
Status MergeUntil(InternalIterator* iter,
CompactionRangeDelAggregator* range_del_agg = nullptr,
const SequenceNumber stop_before = 0,
const bool at_bottom = false,
const bool allow_data_in_errors = false);
// Filters a merge operand using the compaction filter specified
// in the constructor. Returns the decision that the filter made.
// Uses compaction_filter_value_ and compaction_filter_skip_until_ for the
// optional outputs of compaction filter.
CompactionFilter::Decision FilterMerge(const Slice& user_key,
const Slice& value_slice);
// Query the merge result
// These are valid until the next MergeUntil call
// If the merging was successful:
// - keys() contains a single element with the latest sequence number of
// the merges. The type will be Put or Merge. See IMPORTANT 1 note, below.
// - values() contains a single element with the result of merging all the
// operands together
//
// IMPORTANT 1: the key type could change after the MergeUntil call.
// Put/Delete + Merge + ... + Merge => Put
// Merge + ... + Merge => Merge
//
// If the merge operator is not associative, and if a Put/Delete is not found
// then the merging will be unsuccessful. In this case:
// - keys() contains the list of internal keys seen in order of iteration.
// - values() contains the list of values (merges) seen in the same order.
// values() is parallel to keys() so that the first entry in
// keys() is the key associated with the first entry in values()
// and so on. These lists will be the same length.
// All of these pairs will be merges over the same user key.
// See IMPORTANT 2 note below.
//
// IMPORTANT 2: The entries were traversed in order from BACK to FRONT.
// So keys().back() was the first key seen by iterator.
// TODO: Re-style this comment to be like the first one
const std::deque<std::string>& keys() const { return keys_; }
const std::vector<Slice>& values() const {
return merge_context_.GetOperands();
}
uint64_t TotalFilterTime() const { return total_filter_time_; }
bool HasOperator() const { return user_merge_operator_ != nullptr; }
// If compaction filter returned REMOVE_AND_SKIP_UNTIL, this method will
// return true and fill *until with the key to which we should skip.
// If true, keys() and values() are empty.
bool FilteredUntil(Slice* skip_until) const {
if (!has_compaction_filter_skip_until_) {
return false;
}
assert(compaction_filter_ != nullptr);
assert(skip_until != nullptr);
assert(compaction_filter_skip_until_.Valid());
*skip_until = compaction_filter_skip_until_.Encode();
return true;
}
private:
Env* env_;
std::shared_ptr<SystemClock> clock_;
const Comparator* user_comparator_;
const MergeOperator* user_merge_operator_;
const CompactionFilter* compaction_filter_;
const std::atomic<bool>* shutting_down_;
Logger* logger_;
bool assert_valid_internal_key_; // enforce no internal key corruption?
bool allow_single_operand_;
SequenceNumber latest_snapshot_;
const SnapshotChecker* const snapshot_checker_;
int level_;
// the scratch area that holds the result of MergeUntil
// valid up to the next MergeUntil call
// Keeps track of the sequence of keys seen
std::deque<std::string> keys_;
// Parallel with keys_; stores the operands
mutable MergeContext merge_context_;
StopWatchNano filter_timer_;
uint64_t total_filter_time_;
Statistics* stats_;
bool has_compaction_filter_skip_until_ = false;
std::string compaction_filter_value_;
InternalKey compaction_filter_skip_until_;
bool IsShuttingDown() {
// This is a best-effort facility, so memory_order_relaxed is sufficient.
return shutting_down_ && shutting_down_->load(std::memory_order_relaxed);
}
};
// MergeOutputIterator can be used to iterate over the result of a merge.
class MergeOutputIterator {
public:
// The MergeOutputIterator is bound to a MergeHelper instance.
explicit MergeOutputIterator(const MergeHelper* merge_helper);
// Seeks to the first record in the output.
void SeekToFirst();
// Advances to the next record in the output.
void Next();
Slice key() { return Slice(*it_keys_); }
Slice value() { return Slice(*it_values_); }
bool Valid() { return it_keys_ != merge_helper_->keys().rend(); }
private:
const MergeHelper* merge_helper_;
std::deque<std::string>::const_reverse_iterator it_keys_;
std::vector<Slice>::const_reverse_iterator it_values_;
};
} // namespace ROCKSDB_NAMESPACE